Background

Originally conceived of as a means for bridging patients to heart transplantation, the encouraging long-term outcomes of left ventricular assist devices (LVADs) have led to their increased use in the treatment of heart failure, even in cases where transplant candidacy or availability is unlikely. Despite the life-saving aspects of LVAD therapy to support the patient with end-stage heart failure, issues of pump obstruction and thrombosis persist, resulting in an increasing need for emergent device exchanges or deaths from thrombosis.1 This forms a diagnostic dilemma for care providers because there are a variety of clinical syndromes that may mimic this feared complication, yet the treatment options for bona fide pump thrombosis are limited. Although algorithms have been proposed to address this problem in a standardized fashion,2 there remains considerable heterogeneity in the diagnosis and management of pump thrombosis between centers. Where outflow graft obstruction is suspected, vascular ultrasound has previously been used intraoperatively to confirm the presence of outflow graft obstruction.3 However, intravascular ultrasound (IVUS) offers the benefit of confirming obstruction before taking the patient to the operating suite for device exchange. We present a case of HeartMate II LVAD (Thoratec Corporation, CA) thrombosis in which IVUS was used in this very manner; the first reported case of its kind.

Case Report

A 65-year-old female (62 kg) with a history of nonischemic dilated cardiomyopathy, rate-controlled atrial fibrillation with prior cardioembolic stroke, hypertension, and osteoporosis presented with worsening symptoms of decompensated heart failure. Despite a prolonged listing for transplant, a suitable donor was not identified on account of her size, blood group (type O), and sensitization. Consent was obtained to proceed with elective implantation of a HeartMate II LVAD (INTERMACS—Interagency Registry for Mechanically Assisted Circulatory Support—status 3). This was performed along with tricuspid valve annuloplasty and surgical coaptation of the aortic valve leaflets using a Park stitch.4

The postoperative course was complicated by residual right ventricular dysfunction that required a prolonged administration of intravenous inodilators (milirinone and nitric oxide), diuresis with furosemide, and initiation of maintenance therapy with oral sildenafil and furosemide. This strategy was pursued in lieu of mechanically supporting the right ventricle because patients have been known to experience poorer outcomes with biventricular mechanical support. Approximately 2 weeks after implantation, the patient experienced a sudden, yet transient and asymptomatic pump stoppage that resolved spontaneously. This was accompanied by ongoing pulsatility index events that were detectable only on waveform analysis and which resolved after decreasing the pump speed to 8400 rpm. She continued to recover until ≈4 weeks after implantation when her clinical status began to deteriorate with worsening weakness and shortness of breath requiring aggressive diuresis and increases of her VAD parameters. Serum markers were suggestive of hemolysis, and appropriate investigations were performed.2

The diagnostic strategy to determine the cause of the LVAD pump difficulties included an echocardiographic ramp study, computed tomography of the chest, and outflow conduit angiography. The ramp study demonstrated incomplete left ventricular decompression with increased LVAD speed to 10 400 rpm and severe right ventricular dysfunction. This raised suspicions for the presence of an outflow graft stenosis, which became further suspected based on computed tomography scans and conduit angiography demonstrating a narrowing near the aortic anastomosis of the outflow graft (Figure 1). To confirm the severity of this potential stenosis and to clarify its hemodynamic significance, the site was further assessed using IVUS and dual-lumen simultaneous pressure measurement.

Narrowing of the outflow graft near the aortic anastomosis site, indicated by white arrows. Visualized using computed tomography (A) and conduit angiography (B).

Intravascular access was obtained with ultrasound guidance via the right femoral artery, and the outflow graft was successfully catheterized using an Amplatz 1 guiding catheter (Boston Scientific, MA). Simultaneous pressure measurements across the conduit and aorta, taken using a 6-French Langston dual-lumen catheter (Vascular Solutions, MN), revealed a peak-to-peak pressure gradient of 24 mm Hg and mean pressure gradient of 11 mm Hg (Figure 2). An extra S-port guidewire was placed into the mid-segment of the outflow conduit, and the patient was then heparinized with 3000 U intravenously. IVUS (Atlantis SR pro; Boston Scientific) was then used to accurately examine the severity of the stenosis by engaging the outflow graft with the probe under fluoroscopy and gradually withdrawing it back to the outflow anastomosis with the aorta while imaging. This confirmed an ≈50% stenosis at the aforementioned site in the outflow graft (Figure 3; Movie I in the Data Supplement).

Langston catheter measurements showing a significant pressure gradient from the outflow graft to the aorta. The values in blue correspond to the measured aortic pressure, whereas the values in red correspond to the outflow graft pressure.

Percutaneous treatment of the outflow graft stenosis was considered; however, serum markers of hemolysis were elevated consistent with pump thrombosis. Therefore, consent was obtained to proceed with pump exchange and revision of the outflow graft. An errant anastomotic repair suture found to be causing the outflow graft stenosis was cut and released. Pump exchange was performed with no complications, and a thrombus was visually confirmed in the explanted device (Figure 4). After implantation of a new HeartMate II LVAD, echocardiographic analysis demonstrated a decompressed ventricle with pump speeds of 8200 rpm and resolution of the outflow graft stenosis; there was no appreciable pressure gradient across this site. The patient’s postoperative course was generally unremarkable, but prolonged, because she required steady diuresis and physical reconditioning. She was discharged home in stable condition ≈5 weeks after the pump exchange procedure. At most recent postdischarge follow-up clinic visit, the patient was clinically stable now 17 months after her pump exchange procedure.

A thrombus is visualized in the lumen of the explanted left ventricular assist device (LVAD), indicated by the white arrow. The thrombus is located at the inflow portion of the device, proximal to the pump rotor.

This case is the first description of IVUS characterization of the outflow graft of an actively working LVAD. In cases where LVAD outflow graft obstruction is suspected, IVUS may not only help confirm and characterize the nature and severity of an obstruction but is likely more detailed than other traditional modalities. Because surgical management of pump thrombosis is significantly affected by the presence of an outflow graft obstruction, it is a useful adjunct in cases where diagnosis and severity are uncertain.

Disclosures

Dr Arora has received an unrestricted research grant from Pfizer Canada Inc. and honoraria from Mallindkrodt Pharmaceuticals. The other authors report no conflicts.